Variable inductance mechanism



Oct. l, 1940. M. J. KIRK ET Al. 2,216,370

VARIABLE INDUCTANCE MECHANISM EMIS. @su

ATTO R N EY Oat. 1,1940.

M. J.'K|RK ET vARIABL INDUQTANCE v4Filed July 5, 195s MECHANI SM 2 Sheets-Sheet 2 BY/ILM wat@ ATTORNEY a Patented Oct. 1, 1940 UNITED STATES PATENT OFFICE and Joseph C. McGinley, Hinsdale, Ill.,

assignors to Johnson laboratories, Inc., Chicago, Ill.,

a corporation o! Illinois Application July 5, 193s, sensi No. 217,404

' 4 claims (ci. 111-242) Our invention relates to an improved operating mechanism for variable inductance devices, and particularly for that type of devices in which the variation in inductance is secured by moving a core relatively to an inductance coil to change the permeability of the magnetic path of the coil. Our invention is particularly adapted to variable inductances of the kind referred to, which are intended for use in connection with high-frequency apparatus, such as the radio-frequency portions of radio transmitting and receiving apparatus.

This application is a continuation in part of our copending application Serial No. 197,222 iiled March 21, 1938, and is particularly directed to systems of the type there disclosed which are especially adapted for use in superheterodyne. radio receivers.

By our invention We employ iiexible cables connected with the ends of the cores and a common operating mechanism for the cables, such as an operating shaft and drinn structures, carried by the shaft, so that all of the cables may be simultaneously operated by rotating the shaft, and so that by properly designing the operating structure, the cores may be simultaneously moved for tuning purposes in connection with high-irequency resonant circuits. In this manner, we eliminate intermediate carriage structures of all kinds between the operating shaft and the cores,

and by employing the insulating tubular mounting of each' inductance coil as the support for the corresponding core for all of its positions, we produce a structure that is at once effective,

extremely simple, and cheap to manufacture.

Our invention is admirably adapted tothe gang operation of a plurality of variable inductance units, sinceit provides for the simultaneous operation of as many magnetic cores of such units as may be desired, and regardless of the number of cores so operated, the operation of each core is accurately effected and is in no way modied by or dependent upon the operation of any other one of the cores. Thus one core may move through a different distance and at a different rate from the remaining cores, to thereby tune one of the resonant circuits over a diierent irequency range. For example, in a superheterodyne receiver the oscillator circuit, which generally covers a narrower frequency range than that covered by the other resonant circuits, may be made to track with the other. circuits by slightly modifying the means for actuating the oscillator core.

ss Our invention also provides means for continuous tuning over a plurality of frequency ranges in succession, since each movable core may be arranged to cooperate successively with a plurality of coaxially mounted inductance coils.

Our invention will be bestunderstood by ref- 6 erence to the accompanying drawings illustrating preferred embodiments thereof, in which:

Fig. 1 illustrates in plan view a three-coil tuning mechanism;

Fig. 2 isI a horizontal, sectional view taken 10 along the line 2-2 in Fig. 1, excepting that in this iigure the cover of the device is shown in place, whereas in Fig. 1 the cover is removed;

Fig. 3 is a horizontal, sectional view of a part of the structure shown in Fig. 2, taken along the 15 line 3--3 in that gure;

Fig. 4 shows in side elevation and to an enlarged scale, one end portion of one of the magnetic cores shown in Fig. 2;

Fig. 5 is a vertical, sectional view to an en- 20 larged scale of a part of the structure shown in Fig. 1, taken along the line 6 5 in that ilgure;

Fig. 6 shows in planview a modied form of our three-coil tuning mechanism; and

Fig. 7 is ar horizontal, sectional view taken 25 along the line 1-1 in Fig. 6, except that in this figure the cover or the device is shown in place, whereas in Fig. 6 the cover is removed.

Similar numerals refer` to similar parts throughout the several views. 30

As shown in Figs. 1 and 2, the tuning mechanism consists of a casing I0 between the side walls of which strips of insulating material I I and I2 are supported vertically by having their ends shouldered and fitting in corresponding 35 slots in the side walls of the casing, as illustrated in Fig. 5.

The strips II and I2 are provided with aligned apertures through which tubes I3 and I3a of insulating material extend with a sliding fit. Each 40 oi' the tubes I3 and I3a has wound thereon near the strip II an inductance coil Il or Ha, the

' ends of the winding of each coil being connected with terminal clips I5 and I6 supported by the strip II.

It is within the scope of the invention to employ, instead of the single-layer solenoidal coils shown, coils of the universal-wound type in which thev radial depth usually equals or exceeds the axial length. It is also comprehended that one or more additional windings may be wound on each tube I3 or Ila adjacent, or at any desired spacing from, the inductance coils I4 or Ila.

Each tube I3 or Ita contains, with a sliding fit, a magnetic core I1 or I'Ia. Each of the cores 55 I1 and I1a has formed in its ends staples I8 and I9 connected respectively with cables 20 and 2|, the latter extending through the end portions of the corresponding tube I3 or I3a.

As shown in Figs. 1 and 2, the left-hand end of each of the tubes I3 or I3a is provided with a tubular plug 22 of insulating material through which the corresponding cable 2| extends. Adjacent the plugs 22, a sheave roller 23 is pivotally supported by the side walls of the casing I Il, so that its lower surface is substantially in line with the axes of the tubes I3 and I 3a. In the other end of the casing I0, an operating shaft 24 is supported by the side walls of the casing, substantially parallel with the strips II and I2 and also with the roller 23, which shaft carries drums 25 and 25h secured thereto. Drum 25h is somewhat smaller in diameter than are drums 25, and

.tube I3a is therefore not quite parallel with tubes I3, as clearly shown in Fig. 2, in order that the cable 20 which cooperates with drum 25h may be substantially centered in tube I3a. Each of the cables 20 extends axially from the corresponding tube I3 or I3a around one of the drums 25 and 2517 and has its end secured to a tensioning spring 25. Each of the cables 2i extends axially from the plugged end of the tube I3 or I3a to and around the roller 23, and has its end secured to the other end of the tensioning spring 25. As shown in Fig. 3, each cable 20 is secured to its drum 25 or 25h by being doubled and passed through an inclined aperture 25a in the wall of the drum, the doubled projecting portion of the cable being knotted adjacent the side wall of the drum as indicated at 20a. Roller 23 has a reduced diameter at 23a to receive the cable 2I which is attached to core Ila.

As a result of the construction described, the spring 26 maintains a tension at all times on the cables 20 and 2i with which it is connected, this tension preferably being much greater than the force required to move the core I1 or I1a in the tube I3 or I3a, and as a result any rotary movement of the shaft 24 will correspondingly move each core I1 or Ila in its tube I3 or I3a, and therefore move the core relatively to the coil I4 or I4a carried by the tube, and thereby correspondingly change the permeability of the magnetic path of the corresponding coil I4 or I4a.

Since drum 25h is somewhat smaller in diameter than drums 25, core Ila is moved less with respect to coil I4a than are cores I1 with respect to coils I4. Coil I 4a thus is advantageously employed in the oscillator circuit of a superheterodyne radio receiver. By way of example, in a particular receiver covering the frequency range between 540 and 1600 kilocycles and having an intermediate frequency of 455 kilocycles, drum 25b has a diameter approximately 0.67 that of drums 25.

Each of the coils I 4 or I 4a is-illustrated as having its terminals connected with a tuning capacitor 21 or 21a having such an amount of capacitance when adjusted as to produce, with the inductance of the coil I4 or I4a, a resonant circuit tunable over a desired range of frequencies by moving the core I1 or Ila into and out of the coil I4 or I4a. To align the several resonant circuits which are tuned by movement of the cores I1 and I1a, so that they may be simultaneously tuned by the operating mechanism, the cores I1 and I1a may first be aligned mechanically by correspondingly setting the drums 25 and 25h relatively to the shaft 24 by the set screws indicated; then after the capacitors 21 and 21a have i will be no interference between been given the proper adjustment to produce the desired resonant frequency at orl near the highfrequency end of the tuning range, any one of the coils may be adjusted as a whole relatively to its core, by a screw 23 threaded through the front end wall of the casing I 0 and engaging at its inner end the outer end of the plug 22 of the corresponding inductance unit, a light spring 29 being secured to the bottom of the casing and engaging the other end of each tube I3 or I la to hold the plug 22 in engagement with the corresponding adjusting screw 28. The inner end of the screw 28 is preferablypOinted or rounded and in engagement with a corresponding depression in the outer end of the ,plug 22, to prevent displacement of the end of the screw from the end of the plug. If preferred, the coils and cores may be given fixed predetermined positions.

It will be understood that capacitor 21a and inductance coil I4a may have values different from those employed in the remaining circuits in order to secure, in cooperation with the smaller drum 25h, the desired oscillator-circuit frequency range together with proper tracking between the oscillator circuit and the other circuits of the receiver.

Where it is desired to ground the cores I1 and I1a, that result is readily accomplished without in any way interfering with the construction and operation described, by providing a thin and narrow strip of metallic conductor 30, one end of which is electrically connected with the corresponding staple I 8 of each core I1 or I1a which is to be grounded, after which the operating cable 20 is also secured to the staple I8, as illustrated in Fig. 4. The outer end portion of the conducting strip 30 is preferably wound into a spiral form with its end electrically connected with a metal rod 3| extending between the side walls of the casing III and connected therewith by a clamping member 32 which not only electrically connects the strips 30 with the casing I 0, but also prevents angular movement of the rod 3I to disturb the adjustment of the conducting strips 30 relatively to the rod. It will be observed that any desired number of inductance units may be mounted as described and operated by a. single operating shaft in the manner described, and furthermore, that the inductance units may be given any desired lateral spacing, since the casing III may have any desired size, the shaft 24 may have a corresponding length, and as many drums 25 and 25h may be -provided on the shaft as there are inductance units, since the mounting of each inductance unit and the drum structure employed on the operating shaft to move the core of each unit are not dependent in any way on any other inductance unit or any other part of the drum structure used to operate another or others of the inductance units.

As illustrated, the shaft 24 is shown as carrying a pointer 33 for indicating the particular frequency to which the system is receptive at any moment, and an operating knob 34 is also shown secured to the projecting end of the shaft 24. The drums 25 and 25h are preferably of such a diameter that a single rotation of the shaft 24, or even less than one rotation, will effect such movement of the cores as to cover the desired band of frequencies for which the inductance devices are designed, and where this is the case, the portions of the cables 20 and 2i connected with the tensioning springs 26 may readily be located substantially above the tubes I3, so there the cable portions andavo and the inductance units. It is obvious, however, that any desired proportions in this respect may be used, and that the cables may be provided with additional cable-directing rollers or drums in particular cases, if preferred, without in any way modifying the operation'of the invention.

In Fig. 2 we illustrate a cover 35 enclosing the casing I0, the cover being removed in Fig. 1 to disclose the parts contained in the casing.

In Figs. 6 and?, we illustrate a different embodiment of our invention from that shown in Figs. 1 and 2 and described in detail above. In this modification, the construction and operation are in general similar, but drum o, instead of being round and somewhat smaller in diameter than drums 25, is of special shape. In this way, the motion which is imparted to core Ila by rotation of shaft 24 is different from that imparted to cores Il by means of drums 25. The spring 26 serves to maintain nearly the same tension on the cables 20 and 2i, for different angular positions of the drum 25e. The exact shape of drum 25o is determined in any particular case by the electrical requirements for example, for securing tracking between the oscillator circuit and the other circuits of the receiver, and it will be understood that the shape shown in Figs. 6 and '1 is merely illustrative and is not to be taken as in any way limiting the scope of the present invention. By properly coordinating the shape of drum 25e with the values of capacitor 21a and of inductance coil Ha, and with the oscillator core I'la, it is readily possible to secure substantially exact tracking throughout a wide frequency range.

` In one particular receiver, for example, the effective radius of drum 25o was slightly greater than that of drum 25h of Figs. 1 and 2 at the low-frequency end of the tuning range and slightly less at the high-frequency end of the range. Instead of a single roller 23 as shown in Figs. 1 and 2, two coaxial and independently rotatable rollers 23h and 23o are employed, to allow for the difference in rate of travel of the cables 2l attached to cores I1 and Ila.

In addition to its use in s'uperheterodyne radio receivers, the present invention may be employed wherever it is desired to provide a plurality of ganged variable inductance devices, one or more of which is to cover a different inductance range from the remaining units, and also wherever with such ganged variable inductance devices, Whether the inductance ranges of the units thereof are the same or not, it is desired to change the inductances of diierent ones of said units according to different laws of variation. It will be understood that the use of the invention in a superheterodyne radio receiver is referred to herein by way of illustrative example only, and that the invention is by no means limited to this particular application of its principles.

Where inthe specification and claims we use the term cable, we include within the meaning of that term any connecting medium having the strength and flexibility requisite for effecting the operation of the cores in the manner above described, whether the connecting medium be fibrous, metallic or otherwise; it will be understood that where the cores are required to be electrically insulated fromy other parts of the mechanism, the cable material should be of an insulating nature; although where it is desired to electrically connect the cores with other parts of the structure, as, for example, in cases where the cores should be grounded, the cable may be of material that is electrically conductive. In

practice we ilnd cables of braided or woven silk cords quite effective for the purpose described.

Our mechanism above described is adapted for use wherever it is desired to simultaneously vary the inductance of a plurality of inductance units, particularly where it is desirable that the mechanism shall be compact and'of light weight. It is thus well adapted for radio apparatus generally. where it is desired to simultaneously tune resonant circuits by inductance tuning as distinguished from capacitance tuning, since it provides a self-contained compact and multiplestage tuning mechanism which may be assembled as a self-contained unit, in any desired relation and location relatively to the other parts of the transmitting or receiving apparatus, even though the wiring connecting the tuning mechanism with the other parts has substantial length and appreciable capacitance which is added to the iixed capacitance incorporated in the tuning mechanism. For in any such case of fixed assembly of apparatus, the capacitance of the connecting wiring referred to is no disadvantage, since it is made a part of the xed capacitances required in the resonant circuits of the tuning mechanism to cooperate with the variable inductances employed; in fact, such an arrangement in a radio receiver or transmitter has the desirable advantages ofy materially reducing interaction between the component` parts of the apparatus that would otherwise appear in the operation of the apparatus. These advantages are particularly important, for example, in mobile radio receivers for automobile and other uses, where it is desired that the tuning mechanism shall have a location convenient to the operator, and the remainder of the apparatus, such as the tubes and audio-frequency amplifier, shall be at some distance for remote operation and control by the tuning mechanism.

While we have shown our invention in the particular embodimentsabove described, it will be understood that we do not limit ourselves thereto as we may employ equivalents without departing from the scope of the appended claims.

Having thus described our invention, what we claim is:

i. Operating mechanism for variable inductance tuning mechanism having a plurality of inductance coils around corresponding mounting tubes, and having magnetic cores associated with said coils and respectively movable longitudinally in and guided by said tubes'to vary the inductance of said coils for the purpose of station selection from a band of frequencies, which operating mechanism comprises the combination of flexible cables connected directly with the ends of each of said cores to move the same relatively to the corresponding coil, and an operating shaft carrying drums coacting with said cables to simultaneously operate said cores to thereby simultaneously vary the inductances of said coils for tuning purposes at `different frequencies, said drums having differently shaped peripheries differently moving the corresponding cores, the differences in movement of said cores being a curvilinear function of the movement of said operating shaft, whereby by-rotary movement of said shaft the inductances of said coils are changed according to diierent laws of variation.

2. Operating mechanism for variable inductance tuning mechanism having a plurality of inductance coils around corresponding mounting tubes, and having magnetic cores associated with said coils and respectively movable longitudinally in and guided by said tubes to vary the inductance of said coils for the purpose of station selection from a band of frequencies, which operating mechanism comprises the combination of flexible cables connected directly with the ends of each oi' said cores to move the same relatively to the corresponding coil, and an operating shaft carrying drums coacting with said cables to simultaneously operate said cores to thereby simultaneously vary the inductances of said coils for tuning purposes at diiferent frequencies, said drums having di'erently shaped peripheries of different lengths differently moving the corresponding cores, the differences in movement of, said cores being a curvilinear function of the movement of said operating shaft, whereby by rotary movement of said shaft the inductances of said coils are changed according to diiferent laws of variation. Y

3. Variable inductance tuning mechanism including in combination a plurality of mounting tubes, a plurality of inductance coils respectively around said tubes, a magnetic core associated with each of said coils and movable longitudinally in and guided by the corresponding tube to vary the inductance of said coils for tuning purposes at the different frequencies of a tuning band, flexible cables extending respectively and direct- 1y from the ends of said cores to simultaneously operate the same relatively to their respective coils. an operating shaft, a first drum carried by said shaft and having its periphery connected with the flexible operating cables extending from a first one of said cores, a second drum carried by said shaft and having its periphery connected with the flexible operating cables extending from a second one of said cores, said first drum having a different peripheral shape radially from said second drum, whereby the movement of said nrst core is a function of the movement of said shaft differing in kind from the function of movementv :'astaid second core relatively to movement of said 4. Variable inductance tuning mechanism including in combination a plurality of mounting tubes. a plurality of inductance coils respectively around said tubes, a magnetic core associated with each of said coils and movable longitudinally in and guided by the corresponding tube to vary the inductance of said coils for tuning purposes at the different frequencies of a tuning band, flexible cables extending respectively and directly from the ends of said cores to simultaneously operate the same relatively to their respective coils. an operating shaft, a first drum carried by said shaft and having its periphery connected with the flexible operating cables extending from a first one of said cores, a second drum carried by said shaft and having its periphery connected with the flexible operating cables extending from a second one of said cores, said first drum having a different peripheral shape radially and a different peripheral length from said second drum. whereby the movement of said iirst core is a function of the movement oi' said shaft differing in kind and extent from the function of movement of said second core relatively to movement of said shaft.

MARTIN J. KIRK. FREDERICK N. JACOB. JOSEPH C. MCGINLEY. 

